1. Field
Example embodiments relate to a method and a device for controlling a main control valve of construction machinery. More particularly, example embodiments relate to a control method and a control device for controlling a main control valve including at least two control valve devices controlled by one joystick.
2. Description of the Related Art
A hydraulic system in construction machinery may include a joystick. An operator manipulates the joystick to control a corresponding control valve device, thereby driving an actuator connected to the corresponding control valve device.
A general function of a joystick is explained with reference to FIG. 1. FIG. 1 is a view illustrating a joystick capable of controlling two control valves.
A manipulation device includes two joysticks J1 and J2, as illustrated in FIG. 1. The joystick may be manipulated in forward and backward directions and in right and left directions.
On the other hand, the construction machinery may include a linear type actuator and a rotary type actuator. The linear type actuator may operate to extend or retract. The rotary actuator may operate to rotate in clockwise or counterclockwise directions. The actuators may have two opposite motions, respectively.
Accordingly, one joystick J may generate a total of four signals of which two signals are used to operate one actuator, and thus one joystick J may control two actuators.
For example, as illustrated in FIG. 1, one joystick J1 may be used to control a boom and a bucket, and another joystick J2 may be used to control an arm and a swing motor.
If the joystick J, J1 is pulled backward, a boom actuator extends to raise the boom. If the joystick J, J1 is pushed forward, the boom actuator retracts to lower the boom. Similarly, if the joystick J, J1 is moved to the left, a bucket actuator extends to crowd the bucket. If the joystick J, J1 is moved to the right, the bucket actuator retracts to dump the bucket.
If the joystick J, J2 is pulled backward or pushed forward, an arm actuator extends or retracts. Similarly, if the joystick J, J2 is moved to the left or to the right, a swing motor rotates in clockwise or counterclockwise directions to swing an upper swing body.
FIGS. 2 and 3 are hydraulic circuit diagrams illustrating a hydraulic system including two control valve devices.
Referring to FIGS. 2 and 3, a hydraulic fluid is discharged from a pump P. The hydraulic fluid flows through a center bypass line L1. First and second control valve devices 10 and 20 are installed in the center bypass line L1.
A branch hydraulic line L2 branches from the center bypass line L1. Even when an upstream control valve operates, the hydraulic fluid can be supplied to a downstream control valve device through the branch hydraulic line L2. In here, the upstream and the downstream may refer to a relative position towards the pump P in the center bypass line L1.
A third control valve device 30 is installed to control a flow rate of the hydraulic fluid supplied to the second control valve device 20 through the branch hydraulic line L2. For example, when a more hydraulic fluid is required for another actuator, i.e., the boom actuator, the third control valve device 30 is operated. The third control valve device 30 is operated to reduce the flow rate of the hydraulic fluid supplied to the second control valve device 20, and thus, a more hydraulic fluid is supplied to another control valve device. As illustrated in FIG. 2, the third control valve device 30 is operated to reduce the flow rate of the hydraulic fluid supplied to the second control valve device 20 for controlling the bucket actuator, and thus a more hydraulic fluid is supplied to the first control valve device 10 for controlling the boom actuator.
In a convention method of controlling a main control valve, if an operator manipulates the joystick J with no mistakes, any problems may not occur.
However, when an operator manipulates the joystick with an intention to operate only one of the two control valve devices controlled by the joystick J, interference between the control valves may occur.
That is, even though an operator has an intention to operate only one control valve device, the joystick may be manipulated erroneously by an operator.
For example, even though an operator manipulates the joystick J to the left or to the right with an intention to operate only the bucket, the joystick J may be manipulated unintentionally forward or backward. Thus, when the operator has no intention to operate the boom, the boom may be operated unintentionally by the erroneous manipulation of the joystick.
The hydraulic circuit will be explained in detail with reference to FIGS. 2 and 3.
In order to operate the bucket, the joystick J is manipulated so that a bucket crowd pilot pressure (pi Bk cd) or a bucket dump pilot pressure (pi Bk dp) is applied to move a spool of the second control valve device 20. With an intention of the bucket crowd operation, the spool of the second control valve device 20 is shifted, and thus, the hydraulic fluid is supplied to a head-side chamber of the bucket actuator and the hydraulic fluid is discharged from a rod-side chamber of the bucket actuator.
In this case, when the joystick J is pushed unintentionally backward, as illustrated in FIG. 3, a boom up pilot pressure (pi Bm up) is applied to move a spool of the first control valve device 10. Thus, the first control valve device 10 is moved to close the center bypass line L1, the hydraulic fluid is supplied to the second control valve device 20 through the branch hydraulic line L2. That is, the boom may be operated unintentionally.
As mentioned above, even though an operator has an intention of a bucket single operation, the boom is operated unintentionally. The center bypass line L1 is closed and the hydraulic fluid is supplied to the second control valve device 20 through the branch hydraulic line L2, thereby pressure loss. The hydraulic fluid supplied to the second control valve device 20 may be reduced by an amount of the hydraulic fluid supplied to the boom actuator, so that the bucket operates unstably.
Accordingly, even though an operator has no intention to operate the boom, the joystick J is manipulated erroneously and thus the boom may be operated unintentionally and a desired precise bucket operation may not be obtained.
A conventional method of controlling a main control valve will be explained with reference to FIGS. 4 and 5.
FIG. 4 is a flow chart illustrating a conventional method of controlling a main control valve. FIG. 5 is a view illustrating the conventional method in FIG. 4.
A joystick is manipulated and then a joystick displacement amount is inputted to a controller (S110).
The controller receives the joystick displacement amount and then determines whether the received value has an intention to truly perform a single operation or a multiple operation. Even though an operator has an intention to truly perform the single operation, when a multiple joystick displacement amount is received, a minimum threshold criterion is applied. For example, when the maximum displacement amount of the joystick is set to 100%, only a joystick displacement amount of a predetermined value or more, for example, 1% to 5% or more, is determined as a true signal (S120). That is, the joystick displacement amount of less than the predetermined value is determined as a noise signal and is disregarded.
Then, a valve stroke is calculated based on the joystick displacement amount of the predetermined value or more (S130).
Then, after the valve stroke is determined, a command signal for controlling a control valve according to the determined valve stroke is outputted (S140). When the control valve device 10, 20 includes an electronic proportional pressure reducing valve, a current value signal is outputted as the command signal. The control valve device 10, 20 is shifted according to the current signal such that a hydraulic fluid is supplied to a corresponding actuator to perform a desired work.
Control situations in accordance with the conventional method of controlling a main control valve will be explained with reference to FIGS. 6 and 7.
FIG. 6 is a graph illustrating a valve stroke versus a joystick displacement in accordance with the conventional method of controlling a main control valve. FIG. 7 is a graph illustrating an actuator pressure versus a corresponding pump pressure in accordance with the conventional method of controlling a main control valve.
As illustrated in FIG. 6, when an operator manipulated a joystick J with an intention to operate an arm actuator and with no intention to operate a swing motor, a joystick input signal for driving the swing motor was unintentionally generated. As illustrated in FIG. 7, a great difference between a pressure of a pump and a pressure of a cylinder head side (head-side chamber) of a corresponding arm was observed.
This means that a portion of the hydraulic fluid discharged from the pump is supplied to the swing actuator, thereby causing pressure loss.
In the conventional control method of controlling a main control valve, an undesired control valve device may be operated unintentionally and thus a hydraulic fluid may be wasted to thereby decrease fuel efficiency.
The patent document below discloses a general technical concept of controlling a joystick.
[Patent Document]
Korean Patent Publication No. 10-2009-0070167 (2009 Jul. 1.)